Just as important as what to do, what to say, and how to act in an interview is what not to do, what not to say, etc. Here are some tips to help you avoid that fumble.
In an interview, don't:
1) Blame poor performance on past employers, workplaces, bosses, or co-workers. Even if you worked for Satan in Hell, make an attempt to say something pleasant or neutral, such as, "I learned a great deal" or "It was a really hot industry."
2) Discuss personal or academic pursuits, unless you're still clearly in the small talk portion of the interview, unless someone asks you about these directly, or unless you can relate them to the position for which you are interviewing. Hobbies like mountain climbing show persistence.
3) Appear too eager to discuss matters of compensation, hours, or vacation time. These are legitimate questions, but they should take a back seat to discovering whether or not you and the job are a good fit.
4) Show bad posture: don't slouch, tap your feet or splay your legs or arms;
5) Let nervousness after your actions: don't fumble with objects in your hand, rearrange your hair, jiggle pocket change or chew gum.
6) Let your message get muffled: don't slur, don't drop your eyes, or speak too quickly.
7) Fail to have questions when the time comes.
8) Run on too long with answers to questions. Be aware of how the interviewer is responding to what you're saying. If you catch him or her looking bored or staring at you with a glazed or unfocused look, it's probably time to stop talking. If they want to find out more about what you were talking about, they'll ask you to continue.
9) Fail to answer the question you're asked.
10) Don't forget to smile! Remember, you're there at their invitation.